Thursday, December 31, 2015

Tectonic Implications From Ural Russia for the Columbia Supercontinent

U–Pb zircon geochronology and geochemistry of Paleoproterozoic magmatic suite from East Sarmatian Orogen: tectonic implications on Columbia supercontinent


Terentiev et al


Extensive Paleoproterozoic magmatism occurred in the East Sarmatian Orogen (ESO), located at the junction of the Sarmatian and Volga–Ural segments of the East European Craton, generating numerous felsic to mafic-ultramafic complexes. Here we report geochemical and zircon U-Pb age data from a suite of ultramafic–mafic and diorite–granodiorite intrusive rocks from this orogen. SHRIMP U–Pb dating of zircons yielded the following concordant ages for the magmatic suites: (1) 2085 ± 17 to 2093 ± 20 Ma (sub-volcanic high-Mg intrusions of SHMB-like melanorite–melaquartz-diorite–melagranodiorites and quartz-diorite–tonalite–granodiorites); (2) 2072.4 ± 8, 2073 ± 8.3, and 2068 ± 13 Ma (ultramafic–mafic–diorite layered intrusions); (3) 2053 ± 14 to 2058 ± 22 Ma (magnesian–ferroan quartz-diorite–tonalite–granodiorite intrusions) and (4) 2035 ± 18 Ma (ferroan norite–diorite intrusions). The trace and rare earth element geochemistry indicate arc-related features. The enrichment in LREE and LILE in the mafic-ultramafic and diorite-granodiorite suites is correlated with melting of metasomatised lithosphere mantle along with involvement of crustal components in their petrogenesis. The third magmatic event conforms to the age of the post-collision S- and A-granitoids of the region. Our data indicate two major magmatic events in the post-collisional setting, the former immediately after metamorphism with the formation of schistosity in the host rocks, and the latter two during the culmination of the orogenic cycle in the Voronezh Crystalline Massif.

The duration of the Paleoproterozoic orogeny during the collision of the Sarmatian and Volga–Ural segments of the East European Craton is estimated to be approximately 100 million years from ∼2140 to ∼2035 Ma. We propose that the layered orogenic plutons were derived from relatively deeper mantle source, whereas the sub-volcanic rock series are derivatives of the slightly shallow mantle source. The Paleoproterozoic collision in the region broadly coincides with timing of amalgamation of the global supercontinent Columbia.

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